Enhanced practical photosynthetic CO2 mitigation

ABSTRACT

This process is unique in photosynthetic carbon sequestration. An on-site biological sequestration system directly decreases the concentration of carbon-containing compounds in the emissions of fossil generation units. In this process, photosynthetic microbes are attached to a growth surface arranged in a containment chamber that is lit by solar photons. A harvesting system ensures maximum organism growth and rate of CO 2  uptake. Soluble carbon and nitrogen concentrations delivered to the cyanobacteria are enhanced, further increasing growth rate and carbon utilization.

(b) CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication serial No. 60/218,871, filed Jul. 18, 2000.

(c) STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT

[0002] The U.S. Government has a paid up license in this invention andthe right in limited circumstances to require the patent owner tolicense others on reasonable terms as provided for by the terms ofProgram Solicitation Number DE-PS26-99FT40613 awarded by the U.S.Department of Energy.

(d) REFERENCE TO A “MICROFICHE APPENDIX”

[0003] (Not Applicable)

(e) BACKGROUND OF THE INVENTION

[0004] 1. Field of the Invention

[0005] This invention generally relates to gas cleaning systems, andmore specifically to a biologically-based absorbing apparatus and methodto reduce emissions from fossil burning units.

[0006] 2. Description of the Related Art

[0007] The U.S. produces an estimated 1.7 billion tons of CO₂ annuallyfrom the combustion of fossil fuels. CO₂ is a reflector of infraredradiation, so its presence helps “keep” heat in the atmosphere, makingthe surface temperature warmer than if there was no CO₂ in theatmosphere. It is estimated that at present growth rates, CO₂ levels inthe atmosphere will increase from 350 ppmv (at present) to 750 ppmv inas little as 80 years. In fact, to level CO₂ concentrations at 550 ppmv,we will have to reduce net CO₂ emissions by over 60% from 1990 levelsduring the next 100 years.

[0008] Even if an expensive option for CO₂ removal is discovered, whichis by no means a certainty, CO₂ “disposal” is problematic. U.S.industries consume only 40 million tons of CO₂, produced at a much lowerprice than possible by removing CO₂ from flue gas. Therefore, increasedconsumption of CO₂ appears limited, and options for expanded use appearlimited and costly.

[0009] Sequestration of CO₂ in large bodies of water or in deep minesappears to be the most viable present option. However, sending CO₂ intothe ocean or an abandoned mine is a limited solution. There is no knownexact time scale for storage of CO₂; it may be centuries, but it alsomay only be decades. At best, these are temporary solutions. Further,the transportation issues are considerable, even for the less than 30%of all U.S. fossil-fuel burning power plants that are within 100 milesof an ocean. Existing power plants, with capital values in the hundredsof billions of dollars, are at risk if tens of thousands of miles ofspecialized pipelines must be installed to transport separated CO₂.

[0010] The use of ocean-based sinks could present significant problems.It will be necessary to add large amounts of iron to the ocean to usethe vast quantities of CO₂ stored in the sinks, resulting inuncontrolled growth of certain organisms. Weed plankton, the most likelyorganisms to grow, will not provide sufficient nutrients for the foodwebs, and there is a high probability of significant negativeenvironmental impact. In the case of CO₂ stored at the bottom of theocean in lakes, the adverse effects on the ocean-floor ecosystem cannotbe predicted, but are likely to be considerable.

[0011] Another existing option involves biological carbon sequestrationin outdoor ponds. However, there are inherent inefficiencies related tothis solution for CO₂ sequestration, primarily due to the amount ofcyanobacteria that can be grown in a given volume. For example, if2,000,000 m² of photosynthetic surface area is required for 25%reduction of CO₂ emissions from a power plant, that is equivalent toalmost 500 acres of surface. Very few existing plants have 500 acresavailable to them and fewer could afford to convert 500 acres to ashallow lake or raceway cultivator. Also, there are serious questionsabout how to distribute the flue gas (or separated CO₂) into the lakefor maximum growth, not to mention what to do with the gas once itbubbles to the surface. The flue gas would have to be collected againand redirected up a stack to meet other emission requirements. Further,maintaining such a large “lake” during a Midwestern winter would beproblematic.

[0012] Clearly, other approaches for CO₂ control are needed. Research todevelop a robust portfolio of carbon management options, including safeand effective photosynthetic carbon recycling, will enable continued useof coal in electrical power generation. Despite the large body ofresearch in this area, virtually no work has been done to create apractical system for greenhouse gas control, one that could be used withboth new and existing fossil units.

(f) BRIEF SUMMARY OF THE INVENTION

[0013] A method for removing a carbon-containing compound from a flowinggas stream is performed by interposing in the stream a membrane havingphotosynthetic microbes, such as algae and cyanobacteria, depositedthereon. Applying water and nutrients to the membrane sustains thegrowth of the microbes, and increasing the volume of water harvests themicrobes from the membrane.

[0014] The invention also contemplates an apparatus for removing acarbon-containing compound from a flowing gas stream has a membraneinterposed in the stream. The membrane has photosynthetic microbes, suchas algae and cyanobacteria, deposited thereon.

(g) BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0015]FIG. 1 is a diagram illustrating the carbon sequestration process.

[0016]FIG. 2 is a front view illustrating a membrane.

[0017]FIG. 3 is a diagram illustrating a solution supply andrecirculation system.

[0018]FIG. 4 is a diagram illustrating a flue gas flowing over membrane.

[0019]FIG. 5 is a side view in section illustrating the membranearrangement in the hydrating solution delivery system.

[0020] In describing the preferred embodiment of the invention which isillustrated in the drawings, specific terminology will be resorted tofor the sake of clarity. However, it is not intended that the inventionbe limited to the specific term so selected and it is to be understoodthat each specific term includes all technical equivalents which operatein a similar manner to accomplish a similar purpose. For example, theword connected or term similar thereto are often used. They are notlimited to direct connection, but include connection through otherelements where such connection is recognized as being equivalent bythose skilled in the art

(h) DETAILED DESCRIPTION OF THE INVENTION

[0021] Enhanced natural sinks are the most economically competitive andenvironmentally safe carbon sequestration options for fossil-fuelburning power plants, because they neither require pure CO₂, nor incurthe costs (and dangers) of separation, capture, and compression of CO₂gas. Among the options for enhanced natural sinks, optimizing the growthof existing photosynthetic organisms in an engineered system is lowrisk, low cost, and benign to the environment. Additionally, anengineered photosynthesis system has the advantage of being at thesource of the emissions to allow measurement and verification of thesystem effects, rather than being far removed from the emissions source,as is the case with forest-based and ocean-based natural sinks. Theinvention is suitable for application at existing and future fossilunits.

[0022] Even though CO₂ is a fairly stable molecule, it is also the basisfor the formation of complex sugars (food) through photosynthesis ingreen plants, algae, and cyanobacteria. The relatively high content ofCO₂ in flue gas (approximately 14% compared to the 350 ppm in ambientair) has been shown to significantly increase growth rates of certainspecies of cyanobacteria. Therefore, this photosynthetic process isideal for a contained system engineered to use specially selectedstrains of cyanobacteria to maximize CO₂ conversion to biomass andemitting less of the greenhouse gas to the atmosphere. In this case, thecyanobacteria biomass represents a natural sink for carbonsequestration.

[0023] A diagram of the well-understood process of photosynthesis isshown in FIG. 1. Photosynthesis reduces carbon by converting it tobiomass. As shown in FIG. 1, if the composition of typical cyanobacteria(normalized with respect to carbon) is CH_(1.8)N_(0.17)O_(0.56), thenone mole of CO₂ is required for the growth of one mole of cyanobacteria.Based on the relative molar weights, the carbon from 1 kg of CO₂ couldproduce increased cyanobacteria mass of 25/44 kg, with 32/44 kg of O₂released in the process, assuming O₂ is released in a one-to-one molarratio with CO₂. A conservative estimate indicates that a 2,000,000 m²facility powered by collected solar energy could process 25% of theeffluent CO₂ from a 200 MW coal-fired power plant, producing over140,000 tons of dry biomass per year. Dried biomass could be used in theproduction of fertilizer, fermented or gasified to produce alcohols andlight hydrocarbons, or directly as a fuel to meet biomass mandates inpending deregulation legislation. Therefore, a photosynthetic systemprovides critical oxygen renewal along with the recycling of carbon intopotentially beneficial biomass.

[0024] Optimization of this process in the present invention is based ondesign of a mechanical system to best utilize photosynthetic microbes.Photosynthetic microbes are microorganisms, such as algae andcyanobacteria, which harness photons to fix carbon-containing gas intocarbon-based biomass. Cyanobacteria have been chosen as photosyntheticagents, because they are one of only two groups of organisms capable ofgrowing at the fossil-fired environmental temperatures of 50-75° C. Forexample, Cyanidium calderium has been shown to be able to fix CO₂ underthe conditions of the flue gas remediation apparatus at 70-75° C. andbelow. Cyanobacteria are small in size and grow attached to sedimentparticles in thermal streams. This is an essential property for growthin a fixed cell bioreactor. Another advantage to using cyanobacteria isamenability to manipulation in the laboratory and thus to a power plantsetting. Cyanobacteria in general are mechanically robust making themideal organisms for use in bioreactors.

[0025] Referring to FIG. 2, the photosynthetic microbes populate agrowth surface 10 which is composed of a membrane 14 fastened within aframe 12. The information contained in U.S. patent application Ser. No.60/258,168 to Pasic, et al., is incorporated herein by reference. Thegrowth surface 10 shown in FIG. 2 is rectangular, and the membrane 14 istwenty-one inches long by ten and one-half inches wide, mounted in aframe one half inch thick. However, the size of the membrane 14 may varydepending on the requirements of the power plant in which the inventiveapparatus is applied.

[0026] The material selection for the membrane 14 is dictated by themechanical properties necessary for the optimal design in a containmentchamber 16 shown in FIG. 3.

[0027] The membrane 14 should be an inorganic material, such as plastic,to avoid problems with fungi growth. The membrane 14 must be composed ofa material that suits the specific microbe used, being non-toxic to themicrobe and supporting adhesion. It is essential that microbes suppliedto the growth surface 10 be able to grow in the attached state. Thegrowth surface 10 needs to provide reliable structural integrity whenexposed to the flue gas environment.

[0028] The cyanobacteria are distributed evenly over the membrane 14 tomaximize the photosynthetic surface area. Directly pouring a microbialsolution over the membrane 14, applying the solution using a pump or anorganism-entrained water flow through the membrane accomplishes evendistribution.

[0029] The growth surface 10 is introduced to a carbon-containing gas 21when placed in the containment chamber 16, which is in the flow path ofthe gas 21 as shown in FIG. 4. A light source 20 for the microbes usesfiber optics to supply photons for driving photosynthesis. The lightsource 20 may be positioned above the chamber 16 as in FIG. 4, or in aposition relative to the membrane 14 to optimize cyanobacterial growthand carbon dioxide uptake.

[0030] In FIG. 4 each growth surface 10 is oriented in the containmentchamber 16. The growth surface 10 can be oriented at an angle of ninetydegrees relative to the chamber 16, but the angle may vary depending onthe needs of a specific unit. The growth surfaces 10 may be fixed inplace within the chamber 16, movable in increments, or continuouslymovable to optimize exposure to the flue gas. The orientation of thegrowth surface 10 provides minimum power loss due to flow obstructionwhen in the containment chamber 16.

[0031] Experiments were performed at Ohio University using anexperimental system called a Carbon Recycling Facility (CRF), whichsimulates a flue gas environment by having the membrane 14 populatedwith microbes and contained as shown in FIG. 4. Experiments includeweight and visual analysis of the algae grown and harvested.

[0032] Harvesting is the removal of mature photosynthetic microbes fromthe membrane 14 of the growth surface 10. Harvesting is advantageous,because the rate of carbon dioxide consumption decreases as the growthrate of cyanobacteria slows. Therefore, harvesting cyanobacteria to makespace for further growth maximizes carbon dioxide uptake. The harvestingmethod involves flushing the membrane 14 at periodic intervals with alarge volume of liquid. The momentum from the large volume of flushingliquid is sufficient to overcome adhesive forces that hold the microbeson the membrane, so many of the microbes are displaced from the membrane14.

[0033] Harvesting occurs in the containment chamber 16 by a differentialpressure water supply system, which functions as a nutrient deliverydrip system at low delivery pressures and algal harvesting system athigh delivery pressures. Under normal conditions the membrane 14 ishydrated by capillary action. Under harvesting conditions, the fluiddelivery action is increased, creating a high flow sheeting action thatdisplaces a substantial percentage of the microbes from the membrane 14.

[0034]FIG. 5 shows the preferred arrangement for the manifold waterdelivery system within the containment chamber 16. A pipe 25 receivesthe growth solution from the supply line 36. The solution flows to themembrane 14 through an opening 27 in the pipe 25. As shown in FIG. 5, inthe preferred embodiment an edge of the membrane 14 is held in contactwith the inside of the pipe 25, and the rest of the membrane 14 isdraped through the opening 27. Because the membrane has capillarypassages through which the solution can flow, the solution never has tobe sprayed if spraying is desired to be avoided. Instead, capillary flowcan supply solution to the algae through the membrane.

[0035] Harvesting that results in partial cleaning of the membrane 14 ispreferred. Partial cleaning means that after cleaning, enoughcyanobacteria remain adhered to repopulate the membrane 14. This isdesirable to avoid a growth lag, thereby maximizing carbon dioxideuptake in the system. The harvested cells accumulate in a slurry at thebottom of the containment chamber 16. The harvested cells are removed,and fresh growth solution is applied to the young cells that remain onthe membrane 14.

[0036] In an alternative embodiment shown in FIG. 3, harvesting isaccomplished by administering water and the growth medium by a nozzle19, either separately or by the same nozzle 19. Harvesting by thismethod is accomplished through a stream of pressurized water that flowsout the nozzle 19 and onto the membrane 14. The force of the impactdislodges the cyanobacteria from the membrane 14. Sufficient cleaningoccurs when the water stream is set at a shallow incidence angle and arelatively low velocity, for example between 30 and 40 degrees relativeto the growth surface 10. A 90-degree low-flow, full cone whirl nozzleprovides a good balance between covering a large area with the waterjet, and a gentle partial cleaning. A flat-fan nozzle is also effectivewhen swept or rotated across the coverage area.

[0037] Alternatively, or in addition, a solution may be used tochemically promote removal of the microbes from the membrane 14. Mostmicroorganisms have a cation requirement for adhesion, usually calcium(Cooksey and Wigglesworth-Cooksey, 1995). Thus, they can be removed froma surface with calcium ion-complexing agents such as EDTA or EGTA(Cooksey and Cooksey, 1986).

[0038] The partially cleaned membrane 14 can be repopulated withactively growing cells removed while cleaning the membrane 14. Aftercleaning, the slurry of cells and growth solution is agitated todisperse any clumps of algae into individual cells. Then, selectivefiltration of the slurry separates the large microbial cells that areold or dead from the small cells that are young and alive, and the youngactively growing cells are reapplied to the growth surface 10 torepopulate the membrane 14.

[0039] In the alternative embodiment shown in FIG. 3, the microbeswashed from the membrane 14 may be removed, and the growth solution maybe recirculated to the membrane 14 after harvesting. A recirculationsystem can continuously administer the growth solution to the microbes,while they are subjected to the high temperature gas flowing through thecontainment chamber 16. As shown in FIG. 3, a growth solution drippingmanifold 18 is located at the top of the containment chamber 16. Themanifold 18 continuously delivers the growth solution to the algaethrough a solution supply line 36, through which a solutionsupply-isolating valve 37 regulates the flow of solution. The growthsolution accumulates at the bottom of the containment chamber 16.

[0040] The growth solution flows from the containment chamber 16 througha drain line 22. A drain-isolating valve 24 regulates the flow, and thesolution is drained into a lower holding tank 26. A pump isolation valve28 opens a solution recirculation pump 30 and draws the growth solutionfrom the lower holding tank 26, through an inline filter 33, andupwardly to the upper holding tank 38.

[0041] The growth solution is pumped into the upper holding tank 38,where a float 39 and a level switch 40 regulate the level of growthsolution inside. An electric signal line 34 leads from the level switch40 to the solution recirculation pump 30, which is activated when thesolution reaches a predetermined level in the upper holding tank 38.

[0042] The level of solution in the upper holding tank 38 is maintainedconstant by the level switch 40 and the recirculation pump 30.

[0043] An alternative or additional step in the process may includenutrient enhancement and delivery. Cyanobacteria mostly easily fixcarbon and nitrogen in aqueous form. One possible way to increase carbonand nitrogen content is to use technology known as translating slugflow. Using translating slug flow technology increases concentrations ofnutrients, lowers flue gas temperatures, and increases humidity. Slugscreate zones of greatly enhanced gas-liquid mass transfer, putting CO₂and NOx into the water as soluble species for the cyanobacteria. Optimallevels of these nutrients maximize cyanobacterial growth.

[0044] The cyanobacteria react positively to the conditions establishedby a translating slug flow reactor immediately upstream of thebioreactor. Translating slugs, which have leading edges of greatlyenhanced mass transfer, increase the content of soluble carbon andnitrogen in the liquid used to grow the cyanobacteria. Slugs result whenthe gas to liquid flow reaches unstable conditions in nearly horizontalpipes. In fact, a slight vertical inline can substantially increase slugfrequency and thus increase the rate at which CO₂ is transferred to thewater.

[0045] The process of inducing slug flow (gas-liquid mass transfer)results in vastly enhanced CO₂ absorption in the water used to grow thecyanobacteria, and it produces several other advantages. By absorbingCO₂ in the water in the slug flow reactor, the flue gas might never needto come directly in contact with the bioreactor. If the CO₂ is alreadyin solution, then some cyanobacteria do not require gaseous CO₂ forphotosynthesis. This offers the advantage of using less thermo tolerantcyanobacteria, because the water temperature from the slug flow reactoris between 35-40° C. If a dual CO₂ delivery method is used (some in theaqueous phase, some in the gaseous phase), the interaction of largevolumes of cooled water with the flue gas, and the subsequent saturationof the growth surfaces with the enhanced level of soluble carbon andnitrogen increases growth rate of the photosynthetic organism.

[0046] The use of mature cyanobacteria is an advantage to using thisprocess. Mature cyanobacteria can produce value-added products andenergy. One advantageous use for the post-processed cyanobacteria is inthe combustion of cyanobacteria and coal as a blended fuel in fluidizedbed combustion to power Stirling cycle free piston engines. With pendingelectric deregulation legislation requiring as much as 7.5% utilizationrate of biomass, a viable biofuel and method for utilizing that fuelneeds to be found. Dried cyanobacteria have been shown to have asuitable higher heating value, high volatile content, and have suitableignition characteristics to be co-fired with coal in pulverizedcoal-fired generation units.

[0047] Another benefit is oxygen production. Oxygen is a natural productof photosynthesis. If it is assumed that 1 mole of O₂ is formed for eachmole of CO₂ consumed during photosynthesis, then for every kg of CO₂consumed, (32/44) or 0.73 kg of O₂ are produced. This is a significantbenefit.

[0048] Another benefit is the potential for reduction of otherpollutants, sulfur and nitrogen species. In fact, work by Yoshihara etal. (1996) shows considerable nitrogen fixation from NOx species bubbledthrough a bioreactor, one with poorer mass transfer characteristics thanwould be found in the process described here.

[0049] While this process claims carbon sequestration as its goal,carbon is actually being recycled in this process. Carbon recycling isfundamentally different than sequestration, with several advantages. Insequestration, the carbon is no longer available for use. While CO₂ usefor enhanced oil recovery has a benefit, CO₂ or carbon has little use inother forms of sequestration. With photosynthetic carbon recycling,useful carbon-containing biomass and oxygen are produced from the carbondioxide. As described, biomass has a number of beneficial uses,including as a fuel to offset the use of fossil fuels, as a soilstabilizer, fertilizer, or in the generation of biofuels (such asethanol or biodiesel) for transportation use. In addition, the lightcollection and transmission system designed for the preferred embodimentprovides additional electrical power (using the previous exampleparameters) by converting a portion of the filtered infrared spectrumusing photovoltaics.

[0050] A first experiment was performed at 120° F. under controlledparameters of CO₂ concentration. Experiment I was illuminated at 18.25μmol−s⁻¹m⁻² measured at the base of the experimental containment afterthe algae samples were loaded over the screens in the containment. Againthe amount of algae sample loaded over each screen was 3000 ml givingtotal loading of 12000 ml in the reactor. Table 1.1 gives the weightanalysis of 25 ml samples drawn through paper filters for calculation ofthe weight of algae used for testing. TABLE 1.1 Dry weight analyses fortest samples for Experiment I. Filter Weight before Weight after NumberVolume filtering sample filtering sample Difference #1 25 ml 1.7282 gm1.7435 gm 0.0153 gm #2 25 ml 1.6294 gm 1.6455 gm 0.0161 gm #3 25 ml1.8189 gm 1.8368 gm 0.0179 gm #4 25 ml 1.7889 gm 1.8066 gm 0.0177 gm #525 ml 1.7488 gm 1.7663 gm 0.0175 gm Total = 125 ml  0.0845 gm

[0051] The effective amount of algae loaded was 8.112 gm. The simulatedflue gas at 120° F. contained 10.0% O₂, 5.7% CO₂, 700 ppm CO, 1.87 slpmnatural gas and 23.92 slpm air.

[0052] The light intensity passing through the containment was measured(at the bottom of the reactor), as shown in Table 1.2. TABLES 1.2 Lightintensity passing through the containment for Experiment I. Time Lightintensity (hours) mV μmol-s⁻¹m⁻²  0 48.7 18.25 21 51.2 19.19 45 57.621.58 58 67.8 25.41 70 79.2 29.68 77 83.8 31.41 83 88.1 33.02 93 89.833.65 97 91.6 34.33 109  92.6 34.70 118  93.6 35.08 120  94.2 35.30

[0053] The Difference in dry weight of four numbers of screens andinline filter was calculated and effective weight was compared with theweight of algae samples loaded. Table 1.3 tabulates the measured dry anddifferential weights. TABLE 1.3 Weight analysis of screens and filterfor Experiment I. Before trial After trial Difference Screen #1 149.1 gm150.5 gm 1.4 gm Screen #2 155.6 gm 157.3 gm 1.7 gm Screen #3 149.7 gm151.3 gm 1.6 gm Screen #4 151.7 gm 151.4 gm −0.3 gm   Filter 189.1 gm193.6 gm 4.5 gm Total = 8.9 gm

[0054] It was observed during the experiment that Nostoc 86-3 did notchange color and remained green, but with reduced density on thescreens. In addition, the amount of light intensity passing through thecontainment showed a continuous rise with time. The observation alsosupports the decrease in micro algae density as more light passed overthe screens. However, the amount of cyanobacteria obtained after trialwas more than that initially loaded, indicating a positive growth.

[0055] Experiment II was conducted at 120° F. under an illumination of22.11 μmol−s⁻¹m⁻² measured at the base of the experimental containmentchamber after the algae samples were loaded. Again the amount of algaesamples loaded over each screen was 3000 ml giving total loading of12000 ml in the reactor. Table 2.1 displays the weight analysis of 25 mlsamples drawn through paper filters for calculation of the weight ofalgae for testing. TABLE 2.1 Dry weight analysis for test samples forExperiment II. Filter Weight before Weight after Number Volume filteringsample filtering sample Difference #1 25 ml 1.7666 gm 1.7921 gm 0.0255gm #2 25 ml 1.7011 gm 1.7266 gm 0.0255 gm #3 25 ml 1.7402 gm 1.7668 gm0.0266 gm #4 25 ml 1.8402 gm 1.8677 gm 0.0275 gm #5 25 ml 1.6527 gm1.6778 gm 0.0251 gm Total = 125 ml  0.1302 gm

[0056] The effective amount of algae loaded was 12.500 gm. The simulatedflue gas at 120° F. contained 9.5% O₂, 6.0%CO₂, 500ppm CO, 1.73 slpmnatural gas and 21.33 slpm air.

[0057] For this experiment, the illumination was maintained under ON-OFFmode (12 hour cycle) to support the light and dark reactions ofcyanobacterial photosynthesis. The light intensity passing through thecontainment was measured after every 12 hours (at the bottom of thereactor), as shown in Table 2.2 TABLE 2.2 Light intensity passingthrough the containment for Experiment II. Time Light intensity (hours)mV μmol-s⁻¹m⁻²  0 59.0 22.11 12 74.6 27.96 24 73.4 27.51 36 76.4 28.6448 77.7 29.12 60 77.5 29.05 72 74.0 27.74 84 80.4 30.14 96 84.5 31.67108  88.6 33.21

[0058] After 120 hours the growth screens and filter were removed anddried. Table 2.3 tabulates the measured dry and differential weights.TABLE 2.3 Weight analysis of screens and filter for Experiment II.Before trial After trial Difference Screen #1 146.8 gm 151.1 gm 5.3 gmScreen #2 148.1 gm 151.5 gm 3.4 gm Screen #3 150.1 gm 152.8 gm 2.7 gmScreen #4 148.3 gm 151.1 gm 2.8 gm Filter 137.6 gm 145.9 gm 8.3 gm Total= 22.5 gm 

[0059] The light intensity passing through the containment showed acontinuous but gradual rise in jumps at various intervals. It was alsoobserved that the Nostoc 86-3 changes color to light brown. Cellularstudy testified that the species were of consistent size with the batchculture of algae and maintained the filamentous morphology of Nostoc.The species were found to be maintaining healthy coloration and were notdying. These results indicate that species Nostoc 86-3 can tolerate 120°F. as observed from the color of the samples after the experiment.

[0060] While certain preferred embodiments of the present invention havebeen disclosed in detail, it is to be understood that variousmodifications may be adopted without departing from the spirit of theinvention or scope of the following claims.

1. (Cancelled)
 2. (Cancelled)
 3. (Cancelled)
 4. (Cancelled)
 5. A methodfor removing a carbon-containing compound from a flowing gas stream, themethod comprising: (a) interposing at least one membrane in the gasstream; and (b) depositing on the membrane a photosynthetic microbeselected from the group of algae and cyanobacteria.
 6. The method inaccordance with claim 5, further comprising the step of cooling the gasupstream of the membrane.
 7. The method in accordance with claim 6,wherein the temperature of said gas near the membrane is less than about75 degrees Centigrade.
 8. The method in accordance with claim 5, whereinthe temperature of said gas near the membrane is less than about 75degrees Centigrade.
 9. The method in accordance with claim 7, whereinthe temperature of said gas near the membrane is greater than about 50degrees Centigrade.
 10. The method in accordance with claim 5, whereinsaid carbon-containing compound is carbon monoxide.
 11. The method inaccordance with claim 5, wherein said carbon-containing compound iscarbon dioxide.
 12. A method in accordance with claim 11, furthercomprising the step of applying a liquid to said membrane.
 13. Themethod in accordance with claim 12, wherein said liquid is applied witha volume that varies with time.
 14. The method in accordance with claim12, wherein said liquid contains water.
 15. The method in accordancewith claim 14, wherein the water is injected into said membrane.
 16. Themethod in accordance with claim 5, further comprising the step ofilluminating said photosynthetic microbe with a light source for aperiod of time.
 17. The method in accordance with claim 16, wherein saidlight source includes fiber optics.
 18. The method in accordance withclaim 5, wherein said cyanobacteria is Cyanidium.
 19. The method inaccordance with claim 5, wherein said cyanobacteria is Nostoc.
 20. Themethod in accordance with claim 5, wherein said membrane is a polyester.21. The method in accordance with claim 5, wherein said membrane istetraflouroethylene.
 22. The method in accordance with claim 5, furthercomprising the step of moving the membrane.
 23. A method for removingcarbon dioxide from a flowing gas stream, the method comprising: (a)interposing at least one membrane in the gas stream; (b) depositing onsaid membrane a photosynthetic microbe selected from the group of algaeand cyanobacteria; (c) illuminating said membrane with a light source;and (d) flushing said membrane with a liquid to remove saidphotosynthetic microbe from said membrane.
 24. An apparatus for removinga carbon-containing compound from a flowing gas stream, said apparatuscomprising: (a) at least one membrane mounted in said gas stream; and(b) a photosynthetic microbe, selected from the group of algae andcyanobacteria, on said membrane.
 25. An apparatus in accordance withclaim 24, further comprising means for cooling the gas upstream of themembrane.
 26. An apparatus in accordance with claim 25, wherein thetemperature of the gas near said membrane is less than about 75 degreesCentigrade.
 27. An apparatus in accordance with claim 24, wherein thetemperature of said gas near the membrane is less than about 75 degreesCentigrade.
 28. An apparatus in accordance with claim 24, wherein thetemperature of said gas is greater than about 50 degrees Centigrade. 29.An apparatus in accordance with claim 24, wherein said carbon-containingcompound is carbon monoxide.
 30. An apparatus in accordance with claim24, wherein said carbon-containing compound is carbon dioxide.
 31. Anapparatus in accordance with claim 30, further comprising means forapplying liquid to said membrane.
 32. An apparatus in accordance withclaim 31, wherein said means applies the liquid with a volume thatvaries with time.
 33. An apparatus in accordance with claim 31, whereinsaid liquid contains water.
 34. An apparatus in accordance with claim24, further comprising means for injecting a liquid into said membrane.35. The apparatus in accordance with claim 34, wherein the means injectsvariably with time.
 36. An apparatus in accordance with claim 24,further comprising means for illuminating said photosynthetic microbewith a light source for a period of time.
 37. An apparatus in accordancewith claim 36, wherein said light source includes fiber optics.
 38. Theapparatus in accordance with claim 24, wherein said cyanobacteria isCyanidium.
 39. The apparatus in accordance with claim 24, wherein saidcyanobacteria is Nostoc.
 40. The apparatus in accordance with claim 24,wherein said membrane is a polyester.
 41. The apparatus in accordancewith claim 24, wherein said membrane is tetraflouroethylene.
 42. Anapparatus for removing carbon dioxide from a flowing gas stream, saidapparatus comprising: (a) at least one membrane mounted in said gasstream; (b) a photosynthetic microbe selected from the group of algaeand cyanobacteria on said membrane; (c) means for illuminating saidphotosynthetic microbe for a period of time; and (d) means for injectinga liquid into said membrane for providing nutrients for saidphotosynthetic microbe.